The data on time leaving home to go to work were derived from answers to Question 27. This question was asked of people who indicated in Question 23 that they worked at some time during the reference week, and who reported in Question 25 that they worked outside their home. The departure time refers to the time of day that the respondent usually left home to go to work during the reference week. (See "Reference Week.")

Beginning in 2006, the group quarters (GQ) population is included in the ACS. Some types of GQ populations may have departure time distributions that are different from the household population. The inclusion of the GQ population could therefore have a noticeable impact on the departure time distribution. This is particularly true for areas with a substantial GQ population.